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Article

Impact of Microplastic-Amended Soil on Seed Germination of Alfalfa (Medicago sativa) in a Controlled Environment

by
Abigail Tatum
,
Victoria Martin
and
Vanaja Kankarla
*
Department of Marine and Earth Science, The Water School, Florida Gulf Coast University, FGCU Blvd. S., Fort Myers, FL 33965, USA
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(1), 237; https://doi.org/10.3390/agronomy15010237
Submission received: 28 November 2024 / Revised: 30 December 2024 / Accepted: 11 January 2025 / Published: 18 January 2025
(This article belongs to the Topic Innovative Strategies for Enhancing Plant Tolerance to Abiotic and Biotic Stresses and Ensuring Food Safety in Changing Climates)
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Abstract

:
Plastic pollution is a global concern due to its adverse environmental effects. Plastic production and consumption have continued to rise and are expected to double by 2050. Plastic disposal and degradation produce small particles of plastic—less than 5 mm—that can accumulate, infiltrate, or travel through soil, air, water, plants, and the environment. Healthy soil is a system in sync with good physical, chemical, and biological properties capable of supporting life. There is enough research to show the effects of microplastics (MPs) in aquatic environments; however, much is unclear about the effects of MPs on soil and food systems. To address this knowledge gap, two replicated germination experiments were conducted under a controlled environment in a germination chamber at the Water School Lab, Florida Gulf Coast University. The objective of this study was to determine the germination percentage (GP), mean germination time (MGT) and germination index (GI) of alfalfa seeds (Medicago sativa-VNS (variety not stated)) when germinated under two types of MP-treated soils: (1) fiber-fill plastic (FF) at 0.2% and 1% concentration and (2) plastic packaging (PP) at 0.2% and 1% concentration. The experiments were conducted in the germination chamber for 30 days at optimum germination temperatures of 25/18 °C day/night, with a 12-h photoperiod. The physical (texture, structure), chemical (pH, EC, moisture content (MC), and biological (microorganisms count) properties of the soil were analyzed in the laboratory to understand the impact of MPs on soil properties. In conclusion, our research shows MPs have minimal impacts on germination. Soil pH and MC (moisture content) decreased while EC increased across all treatments, and soil texture was negligibly altered. Microbial communities grew significantly across all treatments, showing that MPs can stimulate bacterial growth.

1. Introduction

Driven by its economic allure and versatile applications, plastic has become omnipresent in today’s environment in numerous ways. Fueling both residential and industrial activities, the resulting microplastics pose a threat on a global scale [1,2]. As of now, inadequate recovery processes of plastic waste result in the accumulation of polymer debris in the environment [3]. This accumulation not only contributes to environmental degradation through improper disposal and landfilling but also perpetuates the fragmentation of plastics into smaller nanoplastics that are driven deep into the earth [4,5,6].
Consequently, the emergence of microplastics, defined as particles less than 5 mm in diameter, has garnered significant attention due to their potential adverse impacts on ecosystems and human health [3,7,8,9,10,11]. This fragmentation results in the pervasive presence of microplastics across various environmental matrices, including soil, food, drinking water, and the human body [3,7,12,13,14].
Although initially seen in aquatic environments, research into the effects of microplastics has only recently gained momentum in terrestrial systems [2,15,16]. Substantial quantities of microplastics have been found in soil worldwide, highlighting the urgency for research in the agricultural field, where practices such as plastic mulching and biosolid application have significantly increased over time [16]. Additionally, non-agricultural sources, such as landfills, littering, and atmospheric deposition, also contribute to the increasing release of microplastics into soil, emphasizing the multifaceted nature of this challenge [15].
Boots et al. (2022) [17] underscored the detrimental effects of contaminants on physicochemical processes and soil fauna. Specifically, Guo et al. (2022) [18] noted that microplastics of smaller particle sizes selectively impact microorganisms, leading to a reduction in bacterial and fungal community richness and diversity, thus affecting the terrestrial biogeochemical cycle. Moreover, the infiltration of microplastics into soil-living organisms poses a significant threat to their fitness and survival, highlighting the cascading effects of plastic pollution on soil ecology (Boots et al., 2022) [17]. Research by Lin (2020) [19] further supports arguments for the impact of microplastics on soil fauna, including microarthropods and nematodes, amplifying concerns regarding the integrity of terrestrial ecosystems.
Although microplastic research continues to develop, we recognize a knowledge gap regarding their influence on seed germination, a pivotal stage in the plant life cycle [20]. De Silva (2022) [21] investigated the effects of polyethylene microplastics on the germination and seedling growth of lentils (Lens culinaris) and observed a significant reduction in internal activity with increasing microplastic concentrations, indicating the possibility of dose-dependent adverse effects on seed germination and seedling growth [21]. Considering the perpetual presence of microplastics in the soil, water, and the environment, it is critical to explore interactions between terrestrial soil and seed germination to understand future risks in agriculture.
Alfalfa (Medicago sativa) is a perennial herbaceous crop known for its high-quality forage legume attributes, including its high protein content and biomass production [16,22]. As a legume, alfalfa can improve soil structure through its deep tap root system and enhance nitrogen supply to subsequent crops through efficient biological nitrogen-fixing bacteria, Rhizobium meliloti, in its root nodules. The species is known for moderate sensitivity to salt damage during emergence. It also exhibits high adaptability, thriving in diverse landscapes and growing conditions [23]. The literature shows that the optimum temperature for alfalfa seeds to germinate is between the temperatures of 29 °C and 18 °C (day/night) [24].
We hypothesized that alfalfa seed germination would remain unaffected in microplastic-amended soils at various concentrations, and the seeds would continue to germinate at their optimum temperatures in organic potting soil.
The study aims to investigate the impacts of microplastic-amended soil on alfalfa seed germination and the physical, chemical, and biological properties of this soil. The objectives of this research were to (1) assess the impact of MP-amended soil at two different concentrations on the germination percentage (GP), mean germination time (MGT), and germination index (GI) of alfalfa seeds, as well as to (2) analyze the impact of MP-contaminated soil on soil physical, chemical, and biological properties post-experiment.

2. Materials and Methods

Two replicated germination experiments were conducted in a climate-controlled growth chamber (Percival Scientific) at The Water School, Florida Gulf Coast University (FGCU), Florida, from the 1st week of February to the 1st week of March, and the end of April to the 1st week of May 2023, respectively.
The soil used for this experiment was organic potting soil (certified 100% organic) which was purchased from a local Home Depot in Fort Myers, Florida. Alfalfa (Medicago sativa) organic seeds were purchased from a local vendor (Now Real Food). Seeds were stored under cooler temperatures to avoid any fungal infection or pests for the experiment. Microplastics were prepared by manually cutting bulk plastics into pieces 5 mm or smaller (microplastics (MP)). The experimental research design was a completely randomized design (CRD). The factorials were (1 species) × (1 soil type) × (2 MPs) × (2 conc.) × (4 reps), making up 16 units. Two replicated experiments constituted 32 experimental units overall. Two types of microplastics were used for the experiment: namely, polyester fiberfill (FF) at 0.2% and 1.0% concentration (w/w), and plastic packaging material (PP) at 0.2% and 1.0% (w/w), respectively. The soil was amended with different concentrations of each type of microplastic (MP) by mixing them until there was a proper soil-to-MP ratio in each treatment. Each treatment was replicated four times. MPs FF and PP were mixed with soil at 0.2% (w/w) and 1.0% (w/w) and left to acclimate at room temperature (20–25 °C) for 49 days before the introduction of the alfalfa seeds. Petri plates of 150 mm diameter, each filled with 20 gm of microplastic-contaminated soils, were randomly arranged in the germination chamber. Ten alfalfa seeds per petri plate were placed at half an inch depth in each petri plate inside the microplastic-contaminated soils at various concentrations, irrigated with 2 mL of deionized water at the time of sowing, and allowed to grow in a climate-controlled germination chamber (Percival Scientific) with SciBriteTM LED lighting(Percival Intellus control system, company name is Percival Scientific and is manufactured in Perry, IA, USA) with alternating 25/18 °C day/night temperature for a 12-h photoperiod for 30 days. Photosynthetic photon flux density was approximately 30 mol µm−2 s−1. The petri plates were checked daily for seed germination for 30 days. Seeds were considered germinated with the protrusion of the embryo from the soil and were tossed out, and data was collected daily at the same time each day for 30 days. Additionally, 2 mL of water was added to each petri plate to prevent the soil from drying out. At the end of the 30 days, the germination percentage (GP), mean germination time (MGT), and germination index (GI) were calculated.

2.1. Methods for Soil Physical, Chemical and Biological Properties

2.1.1. Soil pH and Electrical Conductivity Methods

10 g of soil sample from each treatment was diluted by adding 20 mL of deionized water (1:2 ratio) and mixing well. The samples were hand-shaken for 6 min, followed by 6 min of vortexing after activation. Then, the sample suspension was poured into a separately labeled 100 mL graduated cylinder and allowed to sit at room temperature (20–25 °C). Suspension pH and EC were measured using a Ross pH Electrometer and a pen meter (Ohaus Waterproof Pen Meter ST20S), respectively; data was immediately recorded (Table 1).

2.1.2. Soil Texture

Soil texture was analyzed using a Mastersizer 3000 with a Hydro EV dispersion unit (Malvern Panalytical, a spectris company, Worcestershire, UK)to determine particle size distribution and soil composition to establish a classification of soil type using laser diffraction. The refractive index for water was set at 1.33, while the obscuration limits were set at 0.1 to 20. The data from the samples were recorded 5 times for 30 s each, and an average of the data set was used to report values (Table 1).

2.1.3. Soil Moisture Content

Soil moisture was measured using the gravimetric method: taking 10 g of soil from each treatment and then recording their wet weights and dry weights before and after drying samples in an Isotope conventional oven set to 105 °C for 24 h. The moisture content of the soil was then calculated by subtracting the weight of the dry soil from the weight of the wet soil and then dividing by the weight of the wet soil (Table 1).

2.1.4. Soil Microbes

Soil microbes were analyzed using the serial dilution method. This method measures the number of microorganisms per colony forming units (CFUs) in a soil sample. Microbial analysis of treatments was conducted to ascertain how many microorganisms per colony forming units (CFUs) there were of prepared soil types (Table 1). Samples were prepared by weighing 5 g of soil per treatment and diluting them with 45 mL of deionized (DI) water in 50 mL sterile tubes labeled as A 10 − 1 (for a total of five tubes per dilution of treatments). Samples were then shaken for 10 min and, using a micropipette, 1 mL of each sample was transferred to new dilution tubes containing 9 mL of DI water labeled as B 10 − 2 . These were then shaken for another 5 min. This process was repeated twice more to create C 10 − 3 and D 10 − 4 dilution samples by transferring 1 mL of B to C, and the same for C to D. Using a micropipette, 0.1 mL each of sample C 10 − 3 and D 10 − 4 were transferred to their respective agar plates, uniformly dispersing samples with a sterile L stick. Plates were then flipped and parafilmed and stored at room temperature (20–25 °C) for 5 days before colonies were counted. MP treatments stimulated CFU, and microbial communities grew significantly between the pre- and post-experiment periods, suggesting all soil treatments and concentrations were healthy soils. Healthy soils contain 106 to 108 bacteria per gram, and unhealthy soils have <106 CFU [25].

Initial Soil Properties

Some of the initial bio-geo-chemical properties of the soil used in this experiment are shown below.

2.2. Statistical Analysis

The data on seed germination and soil properties were analyzed using a single-factor ANOVA followed by Tukey’s Honest Significant Difference (HSD) post-hoc test. The analysis of variance (ANOVA) provided significant results, which helped to identify the difference between the groups; results indicated that at least one group differs from the other groups [26]. The Tukey–Kramer method, using the Studentized Range distribution, was used to compute the adjustment to the critical value [27]. The statistical significance of the analysis was defined at p < 0.05.

3. Germination Experiments

Germination Variables

The effect of microplastic-amended soil on seed germination of the studied species was evaluated using the parameters germination% (G%), mean germination time (MGT), and germination index (GI) [28]
These parameters were calculated using the following equations:
G % = S e e d s   g e r m i n a t e d T o t a l   s e e d s × 100
MGT = ∑(𝑛𝑖𝑡𝑖)/∑(𝑛𝑖)
GI = ∑|20 − ti)/ni|/S
where ni represents the number of newly germinated seeds on day I; ti is the number of days from the start of the experiment till today I; S represents the total number of seeds in an experimental unit (germinated/emerged/viable/non-germinated/non-emerged); and 30 days were spent in the germination experiment test plus 1.

4. Results and Discussion

4.1. Germination Percentage (GP%)

The results showed that the number of seeds germinated within and between the treatments was insignificant. The germination percentage (GP) of all treatments of both replicates showed no significant differences. However, FF 0.2% displayed 3 ± 1.4 units higher GP in comparison with the control (without MPs), while FF 1.0% had the lowest GP (Figure 1). This tells us that the type of MP (FF in this case) and its lower concentration (0.2%) encouraged seed germination and that increasing its concentration (1.0%) impacted the seed germination process. One would also agree that irrespective of the MP type, the treatments with a lower concentration of MPs at (0.2%) showed a higher seed germination rate.
Lozano (2022) [29] did not find differences in the final GP between treatments with MPs and a control. However, other studies have observed reduced final GP when exposed to microplastics [30,31]. Interestingly, FF 0.2% showed the highest GP (100%) across both replicates. This is contradictory to other findings that indicate that clothing (polyester) microfiber reduces seed germination [32]. Regardless, the results of our research indicate that MPs show no significant impact on GP within our experimental conditions.
More than 25 different studies on microplastics and nanoparticles have displayed exposure of ≤1 day decreased seed germination by approximately 17%, while exposure for 2–4 days and greater than 4 days has no significant effects on germination [33]. Seeds of certain plant species may adapt to MP particles and/or leached additives after a certain amount of exposure time. Also, it is apparent that seeds of different plant species react differently to MP contamination for their germination parameters, and therefore, more research is needed to explore this relationship.

4.2. Mean Germination Time (MGT)

An overall significance was assessed between measurement periods for MGT. However, there was no statistically significant difference in MGT between individual treatments when compared to the control. The mean germination time computes the rate and time-spread of the germination of seeds; accordingly, the lower the MGT, the faster a population of seeds reaches germination [34,35]. Though not significant, FF 1.0% showed a higher MGT (1.87 ± 0.04) compared to the rest of the treatments (Table 2). Microplastics, FF 0.2%, and PP 0.2% of both replicates displayed the lowest MGT, indicating that the population of seeds for that treatment germinated quickly compared to other treatments (Figure 2). Sahasa (2023) [20] found similar results when black gram (Vigna mungo L.) and tomato (Solanum lycopersicum L.) seeds were exposed to MPs, and MGT showed no significant differences for either species. Another study found MPs of varying sizes either had insignificant impacts on MGT or decreased the MGT of soybeans (Glycine max), irrespective of their concentrations [36]. The size of the MPs could have a more substantial impact on germination parameters than previously thought.

4.3. Germination Index

An overall significance was assessed between all treatments and replicates for the GI parameter. GI is the most comprehensive measurement parameter, combining both GP and speed (spread, duration, and ‘high/low’ events) [37]. A higher GI value denotes a higher percentage and rate of germination [38]. Data analysis revealed that GI values had the highest variation among MP treatments, most likely due to the range of the data (Table 3). The mean GI of FF 1.0% showed the lowest GI within and between the replicates, having a significantly lower GI (1.34 ± 0.11 × 10−1) than all other treatments (Figure 3). Results from another study showed a decrease in GI in soybeans, specifically in treatments where MP concentrations were higher, but an insignificant effect on GI for mung bean seeds for all treatments [36]. This could indicate that certain species are more resilient or adaptive to stressors such as MPs.

4.4. Changes in Soil Physical Chemical and Biological Properties (Pre-Post Experiment)

Soil characteristics, such as soil pH, EC, soil moisture content, and soil microbes, were analyzed before and after 30 days of completing the germination experiments.

4.4.1. Soil pH and Electrical Conductivity

Soil pH decreased in the range of 8.3 to 7.7 across all the treatments with the addition of microplastics. Initial pH readings of treatments were slightly more alkaline compared to post-experiment soil pH readings. Studies have shown soil pH decreases after 30 days of exposure to high-density polyethylene [30,39,40].
Soil EC increased in all treatments post-experiment.

4.4.2. Texture and Soil Moisture Content

Soil texture remained the same and soil moisture lowered considerably compared to initial measurements across all treatments. It is possible that the alteration of soil particle compositions after the final measurement for MPs could have impacted soil water content. It was evident that the soil structure was affected by the type and concentration of microplastics because the soil aggregate size fraction lowered the soil moisture holding capacity of the soil, as was observed in our results. The presence of MPs in soils can weaken soil-water holding capacity in loamy sand and silty loam soils [41,42]. Studies by Qi (2020) and Guo et al., (2022) [18,43] found increasing microplastics in the soil closed several soil micropores and reduced the soil water-holding capacity, although there was no apparent dose-dependent response in this study. Other studies have shown that polyester fibers can significantly reduce soil aggregate stability as well as water-holding capacity [43,44]. One factor contributing to this decrease in water-holding capacity can most likely be attributed to the strong hydrophobicity of MPs [3].

4.4.3. Soil Microbes

Microbial data is shown in Table 4. All treatments demonstrated an increase in bacterial colonies after prolonged exposure to MPs. Healthy colonies contain 10 6 to 10 8 bacteria per gram, while unhealthy soil contains less than 10 6 CFU (colony forming units) [45]. After the final bacterial count, all soils were determined to be healthy based on the total amount of microorganisms per treatment sample. After the final count, soil treatment FF 1.0% contained the highest number of microbes while PP 0.2% contained the lowest number. The initial microbial count of FF 1.0% was also higher than that of PP 0.2%, demonstrating a consistent trend across measurement periods. Initial colony counts determined the control soil to contain only a healthy amount of soil microbes before the seeds were sown. Microbial communities in the control soil showed the least alteration due to a lack of MPs. Within this experiment, MPs did exhibit a stimulating effect on microorganisms; however, the exact mechanism is somewhat unclear. The constituents of soil microorganisms, such as microbial community diversity, have often been identified as sensitive indicators of biological indices for maintaining soil health and quality [46]. Microplastics can change microbial community composition by up-regulating or down-regulating a particular group of microbes [20,44,47,48]. Similar to our results, some studies have observed that microplastics stimulate microbial and enzyme activities in soils [23,44,49]. A mutual interaction exists between MPs and soil enzymes, and some enzymes may react with the chemical bonds of the MPs to induce hydrolysis or redox reactions [50]. Microbial community diversity could be distinct and vary under certain conditions, where microorganisms could utilize MP particles as a niche habitat. This is because microplastics would contain different additives, including functional additives (stabilizers, flame retardants, plasticizers, lubricants, foaming agents, biocides, etc.), colorants (pigments, azo colorants, etc.), fillers (mica, kaolin, calcium carbonate, etc.), and reinforcements (e.g., glass and carbon fibers), added during the plastic production process [51,52]. Microbes in soil ecosystems could adhere to MPs similarly to soil aggregates if conditions and MP characteristics allowed for it. It is worth noting that other studies have found that MP contamination decreased microbial communities, contrary to this study’s findings. The variation in reported findings can be attributed to differences in types of MPs, such as shape, size, plastic additives, and soil particle composition.

5. Conclusions

Microplastics have varying effects on soil properties and seed germination parameters according to the results from this study. Soil texture and particle composition were minimally altered, though alterations may have impacted soil water retention. Soil pH tended to be slightly more acidic, EC increased significantly, soil texture remained the same, and soil moisture lowered considerably in all MP treatments after 30 days post-experiment. It is interesting to note an increase in microbial communities post-experiment after prolonged exposure to MPs in all the treatments. It was evident from our results that MPs enabled the growth of microbial communities, providing healthy soil for better seed germination. This indicates a possible correlation between microbial growth stimulation and prolonged exposure to MPs. It is possible that certain of the experimental factors or materials used could have influenced the impact of MPs on the germination parameters and soil properties. Irrespective of the MP type, lower concentrations (0.2%) of FF and PP had relatively low or no significant impact on seed germination. In all MP treatments, the seeds displayed above 90% germination, with a slight decrease if we increased the MP concentration from 0.2 to 1.0%. Treatments with low MP concentrations led to high seed germination percentages across all treatments. Only one treatment, i.e., FF 1.0%, produced significant differences in GI and MGT among all other treatments. Overall, increasing the MP concentration from 0.2% to 1.0% negatively impacted the GP, MGT, and GI. Variations in MP composition, size, shape, and additives make determining the effects of MPs difficult. Microplastic contamination in current terrestrial environments can vary drastically depending on the region, soil composition, plastic-type and size, contaminant source, and other influencing variables. This was a very brief experiment, and further research is needed to explore all potential MP impacts on terrestrial systems due to various unknown and contrasting reports.

Author Contributions

Conceptualization: V.K.; Methodology: V.K.; Software: A.T. and V.M.; Validation: V.K.; Formal analysis: A.T., V.M. and V.K.; Investigation: A.T., V.M. and V.K.; Writing (Original draft preparation): A.T. and V.M.; Writing (review and editing): A.T., V.M. and V.K.; Visualization: V.K.; Supervision: V.K.; Project administration: V.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by The Water School, FGCU (Florida Gulf Coast University) Florida.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

We thank The Water School, FGCU (Florida Gulf Coast University) FL for their funding, Ajpaal Kalyanmasih for the field help, and Haruka Urakawa for lab assistance during this project.

Conflicts of Interest

The authors declare no conflicts of interest. The funders have no role in the design of the study; in the collection, analysis, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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Agronomy 15 00237 g001
Figure 1. Graphical representation of germination percentage of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with the same lowercase letters are not significantly different (Tukey’s HSD test, p < 0.05).
Figure 1. Graphical representation of germination percentage of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with the same lowercase letters are not significantly different (Tukey’s HSD test, p < 0.05).
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Figure 2. Graphical representation of the mean germination time of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with same lowercase letters are not significantly different (Tukey’s HSD test, p < 0.05).
Figure 2. Graphical representation of the mean germination time of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with same lowercase letters are not significantly different (Tukey’s HSD test, p < 0.05).
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Figure 3. Germination index of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with the same lowercase letters are not significantly different. (Tukey’s HSD test, p < 0.05).
Figure 3. Germination index of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with the same lowercase letters are not significantly different. (Tukey’s HSD test, p < 0.05).
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Table 1. pH: hydrogen ion concentration in a solution; EC: electrical conductivity; MC: moisture content; CFU: colony forming units.
Table 1. pH: hydrogen ion concentration in a solution; EC: electrical conductivity; MC: moisture content; CFU: colony forming units.
ColorStructureTexture (%)pHEC (dS/m)MC (%)Microbial Count (CFU)
SandSilClay
10 YR 2/2Granular2.097.01.08.3719.5756.91.7 × 106
Table 2. Mean germination time (MGT) of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with the same lowercase letters are not significantly different. (Tukey’s HSD test, p < 0.05).
Table 2. Mean germination time (MGT) of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with the same lowercase letters are not significantly different. (Tukey’s HSD test, p < 0.05).
TreatmentMean Germination Time (MGT) in Days
Control1.70 ± 0.12 (ab)
FF 0.2%1.53 ± 0.06 (a)
FF 1.0%1.87± 0.04 (b)
PP 0.2%1.61 ± 0.07 (ab)
PP 1.0%1.66 ± 0.07 (ab)
Table 3. Germination index of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with the same lowercase letters are not significantly different. (Tukey’s HSD test, p < 0.05).
Table 3. Germination index of alfalfa in soils with four MP treatments. Results are the mean ± SEs (standard errors). Means with the same lowercase letters are not significantly different. (Tukey’s HSD test, p < 0.05).
TreatmentGermination Index
Control7.06 ± 0.38 (a)
FF 0.2%7.60 ± 0.22 (a)
FF 1.0%5.72 ± 0.27 (b)
PP 0.2%6.94 ± 0.22 (a)
PP 1.0%6.78 ± 0.2 (a)
Table 4. Microbial count between measurement periods (pre- and post-experiment). The sum of microbes in dilutions (C 10−3 and D 10−4) equals the total microbes in treatment soils. CFUs (colony-forming units) are used to determine soil health. Means with the same lowercase letters are not significantly different (Tukey’s HSD test, p < 0.05).
Table 4. Microbial count between measurement periods (pre- and post-experiment). The sum of microbes in dilutions (C 10−3 and D 10−4) equals the total microbes in treatment soils. CFUs (colony-forming units) are used to determine soil health. Means with the same lowercase letters are not significantly different (Tukey’s HSD test, p < 0.05).
Initial Microbial Count (Pre-Experiment)
TreatmentsC 10−3D 10−4TotalCFUClassification
Control72,0001,100,0001,172,0001.17 × 106Healthy Soil
FF MP 0.2%51,000460,000511,0005.11 × 105Unhealthy Soil
PP MP 0.2%69,000810,000879,0008.79 × 105Unhealthy Soil
FF MP 1.0%69,000850,000919,0009.19 × 105Unhealthy Soil
PP MP 1.0%61,000770,000831,0008.31 × 105Unhealthy Soil
Final Microbial Count (Post-Experiment)
TreatmentsC 103D 104TotalCFUClassification
Control307,0001,470,0001,777,0001.78 × 106Healthy Soil
FF MP 0.2%318,0002,600,0002,918,0002.92 × 106Healthy Soil
PP MP 0.2%167,0001,590,0001,757,0001.76 × 106Healthy Soil
FF MP 1.0%286,0002,850,0003,136,0003.14 × 106Healthy Soil
PP MP 1.0%174,0002,210,0002,384,0002.38 × 106Healthy Soil
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Tatum, A.; Martin, V.; Kankarla, V. Impact of Microplastic-Amended Soil on Seed Germination of Alfalfa (Medicago sativa) in a Controlled Environment. Agronomy 2025, 15, 237. https://doi.org/10.3390/agronomy15010237

AMA Style

Tatum A, Martin V, Kankarla V. Impact of Microplastic-Amended Soil on Seed Germination of Alfalfa (Medicago sativa) in a Controlled Environment. Agronomy. 2025; 15(1):237. https://doi.org/10.3390/agronomy15010237

Chicago/Turabian Style

Tatum, Abigail, Victoria Martin, and Vanaja Kankarla. 2025. "Impact of Microplastic-Amended Soil on Seed Germination of Alfalfa (Medicago sativa) in a Controlled Environment" Agronomy 15, no. 1: 237. https://doi.org/10.3390/agronomy15010237

APA Style

Tatum, A., Martin, V., & Kankarla, V. (2025). Impact of Microplastic-Amended Soil on Seed Germination of Alfalfa (Medicago sativa) in a Controlled Environment. Agronomy, 15(1), 237. https://doi.org/10.3390/agronomy15010237

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